This invention relates to positive temperature coefficient ceramic resistors.
Positive temperature coefficient resistors are devices whose resistance increases with increasing temperature. Metals very weakly exhibit this property whereas doped-BaTiO.sub.3 -based ceramics exhibit a much stronger positive temperature coefficient characteristic. These barium titanate ceramics are used for temperature sensing, switching, current stabilization, and self regulating heating. See, for example, U.S. Pat. No. 4,086,467, which discloses a self-regulating heater utilizing barium titanate. These ceramics are, however, limited to operating temperatures below 300.degree. C. and typically below 250.degree. C. See, "Ceramic Materials for Electronics", ed. Relva C. Buchanan, Marcel Dekker, Inc., Chapter 5 (1986). It is also known that chromium-doped vanadium sesquioxide, (V,Cr).sub.2 O.sub.3, exhibits a positive temperature coefficient characteristic. This material has a transition from low to high resistivity at around 80.degree. C.